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Java interview questions-8 (Interfaces and String handling)
Posted Date: 19 Dec 2007 Resource Type: Articles/Knowledge Sharing Category: Study Abroad
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Posted By: BHARATH Member Level: Gold
Rating:  Points: 5
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* this is very important *
Inheritance:-
1) What is the difference between superclass & subclass?
Ans : A super class is a class that is inherited whereas subclass is a class that does the inheriting.
2) Which keyword is used to inherit a class?
Ans : extends
3) Subclasses methods can access superclass members/ attributes at all times?
True/False
Ans : False
4) When can subclasses not access superclass members?
Ans : When superclass is declared as private.
5) Which class does begin Java class hierarchy?
Ans : Object class
6) Object class is a superclass of all other classes?
True/False
Ans : True
7) Java supports multiple inheritance?
True/False
Ans : False
8) What is inheritance?
Ans : Deriving an object from an existing class. In the other words, Inheritance is the process of inheriting all the features from a class
9) What are the advantages of inheritance?
Ans : Reusability of code and accessibility of variables and methods of the superclass by subclasses.
10) Which method is used to call the constructors of the superclass from the subclass?
Ans : super(argument)
11) Which is used to execute any method of the superclass from the subclass?
Ans : super.method-name(arguments)
12) Which methods are used to destroy the objects created by the constructor methods?
Ans : finalize()
13) What are abstract classes?
Ans : Abstract classes are those for which instances can’t be created.
14) What must a class do to implement an interface?
Ans: It must provide all of the methods in the interface and identify the interface in its implements clause.
15) Which methods in the Object class are declared as final?
Ans : getClass(), notify(), notifyAll(), and wait()
16) Final methods can be overridden.
True/False
Ans : False
17) Declaration of methods as final results in faster execution of the program?
True/False
Ans: True
18) Final variables should be declared in the beginning?
True/False
Ans : True
19) Can we declare variable inside a method as final variables? Why?
Ans : Cannot because, local variable cannot be declared as final variables.
20) Can an abstract class may be final?
Ans : An abstract class may not be declared as final.
21) Does a class inherit the constructors of it's super class?
Ans: A class does not inherit constructors from any of it's super classes.
22) What restrictions are placed on method overloading?
Ans: Two methods may not have the same name and argument list but different return types.
23) What restrictions are placed on method overriding?
Ans : Overridden methods must have the same name , argument list , and return type. The overriding method may not limit the access of the method it overridees.The overriding method may not throw any exceptions that may not be thrown by the overridden method.
24) What modifiers may be used with an inner class that is a member of an outer class?
Ans : a (non-local) inner class may be declared as public, protected, private, static, final or abstract.
25) How this() is used with constructors?
Ans: this() is used to invoke a constructor of the same class
26) How super() used with constructors?
Ans : super() is used to invoke a super class constructor
27) Which of the following statements correctly describes an interface?
a)It's a concrete class
b)It's a superclass
c)It's a type of abstract class
Ans: c
28) An interface contains __ methods
a)Non-abstract
b)Implemented
c)unimplemented
Ans:c
STRING HANDLING:-
Which package does define String and StringBuffer classes?
Ans : java.lang package.
Which method can be used to obtain the length of the String?
Ans : length( ) method.
How do you concatenate Strings?
Ans : By using " + " operator.
Which method can be used to compare two strings for equality?
Ans : equals( ) method.
Which method can be used to perform a comparison between strings that ignores case differences?
Ans : equalsIgnoreCase( ) method.
What is the use of valueOf( ) method?
Ans : valueOf( ) method converts data from its internal format into a human-readable form.
What are the uses of toLowerCase( ) and toUpperCase( ) methods?
Ans : The method toLowerCase( ) converts all the characters in a string from uppercase to
lowercase.
The method toUpperCase( ) converts all the characters in a string from lowercase to
uppercase.
Which method can be used to find out the total allocated capacity of a StrinBuffer?
Ans : capacity( ) method.
Which method can be used to set the length of the buffer within a StringBuffer object?
Ans : setLength( ).
What is the difference between String and StringBuffer?
Ans : String objects are constants, whereas StringBuffer objects are not.
String class supports constant strings, whereas StringBuffer class supports growable, modifiable strings.
What are wrapper classes?
Ans : Wrapper classes are classes that allow primitive types to be accessed as objects.
Which of the following is not a wrapper class?
String
Integer
Boolean
Character
Ans : a.
What is the output of the following program?
public class Question {
public static void main(String args[]) {
String s1 = "abc";
String s2 = "def";
String s3 = s1.concat(s2.toUpperCase( ) );
System.out.println(s1+s2+s3);
}
}
abcdefabcdef
abcabcDEFDEF
abcdefabcDEF
None of the above
ANS : c.
Which of the following methods are methods of the String class?
delete( )
append( )
reverse( )
replace( )
Ans : d.
Which of the following methods cause the String object referenced by s to be changed?
s.concat( )
s.toUpperCase( )
s.replace( )
s.valueOf( )
Ans : a and b.
String is a wrapper class?
True
False
Ans : b.
17) If you run the code below, what gets printed out?
String s=new String("Bicycle");
int iBegin=1;
char iEnd=3;
System.out.println(s.substring(iBegin,iEnd));
Bic
ic
c) icy
d) error: no method matching substring(int,char)
Ans : b.
18) Given the following declarations
String s1=new String("Hello")
String s2=new String("there");
String s3=new String();
Which of the following are legal operations?
s3=s1 + s2;
s3=s1 - s2;
c) s3=s1 & s2
d) s3=s1 && s2
Ans : a.
19) Which of the following statements are true?
The String class is implemented as a char array, elements are addressed using the stringname[] convention
b) Strings are a primitive type in Java that overloads the + operator for concatenation
c) Strings are a primitive type in Java and the StringBuffer is used as the matching wrapper type
d) The size of a string can be retrieved using the length property.
Ans : b.
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